Referring to FIG. 1, a conventional absolute readout apparatus includes an encoder device 11, a readout device 12 and a processing unit 13. The encoder device 11 is spaced apart from the readout device 12, and is movable relative to the readout device 12 in a moving direction (X). The encoder device 11 includes an absolute magnetic track 111 and an incremental magnetic track 112 which are disposed side-by-side and each of which extends in the moving direction (X). The absolute magnetic track 111 has a plurality of absolute-track magnetized regions 113 that form multiple absolute-track boundaries 114 thereamong. The absolute-track boundaries 114 are formed equidistantly along the moving direction (X). The incremental magnetic track 112 has a plurality of first incremental-track magnetized regions 116 with first magnetic polarity and a plurality of second incremental-track magnetized regions 117 with second magnetic polarity that differs from the first magnetic polarity. The first incremental-track magnetized regions 116 and the second incremental-track magnetized regions 117 are arranged alternately and form multiple incremental-track boundaries 115 thereamong. The incremental-track boundaries 115 are formed equidistantly along the moving direction (X). The readout device 12 includes a plurality of digital Hall sensors 121 that correspond to the absolute magnetic track 111 and that are arranged equidistantly along the moving direction (X), and a magnetoresistive sensor 122 that corresponds to the incremental magnetic track 112. The processing unit 13 is electrically coupled to the digital Hall sensors 121 and the magnetoresistive sensor 122.
The digital Hall sensors 121 are configured to sense magnetic fields of the absolute-track magnetized regions 113 that correspond in position thereto for the processing unit 13 to perform decoding thereon to obtain current absolute position information of an object (e.g., metrology systems, motion systems, CNC Mills, semiconductor steppers, etc.) mounted with the encoder device 11. The magnetoresistive sensor 112 is configured to sense movement amount of the first incremental-track magnetized regions 116 and the second incremental-track magnetized regions 117 by magnetic sensing for the processing unit 13 to obtain displacement information of the encoder device 11.
As depicted in FIG. 2, when the abovementioned digital Hall sensors 121 are exactly aligned with the absolute-track boundaries 114, at one or more of which the magnetic field reverses, the magnetic fields of the absolute-track magnetized regions 113 (i.e., the magnetic flux densities) may be too small so the magnetic fields actually sensed by the digital Hall sensors 121 may not come from the correct absolute-track magnetized regions 113 (for instance, assuming that the digital Hall sensors 121 supposedly should each sense the magnetic field of the absolute-track magnetized region 113 immediately to its left, but in reality the magnetic field sensed by one of the digital Hall sensors 121 may come from the absolute-track magnetized region 113 immediately to its right instead), resulting in misreading of the absolute position information.